tailieunhanh - Modern Developments in X-Ray and Neutron Optics Episode 11

Tham khảo tài liệu 'modern developments in x-ray and neutron optics episode 11', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | 398 M. Jergel et al. a b Fig. . Cross-sectional HR TEM images of the as-deposited a and collapsed b Ni C ML whose XRR and GIXDS simulation parameters are given in Table . Black bars at the bottom correspond to 10 nm a and 20 nm b energy-dispersive X-ray and electron diffraction analyses while the matrix is formed by C and a small fraction of fine granular fcc Ni. Obviously the annealing stimulates the growth and coalescence of the original Ni grains found in the as-deposited state which governs also interface morphology as reflected in an increase of the lateral correlation length and a decrease of the vertical correlation of the interface roughness decay of interface conformity . As soon as Ni grains are well developed and the ML becomes discontinuous diffusion of C along Ni grain boundaries may also contribute to the ML breakdown. A complete diffusion of C into Ni layers was reported in the past 21 . The observed thermal stability is comparable to sputtered and PLD Ni C mirrors 18 19 25 . It is worth noting that the ML period steadily increases and C layer densities decrease when increasing the temperature above 100 C. Similar effects were reported in sputtered Ni C MLs with larger periods 21 42 and were attributed to a transformation of the amorphous into the graphitic-like structure. Although we were not able to trace this effect directly by HR TEM or X-ray diffraction due to very thin C layers the observed growth and coalescence of Ni grains connected with a long-distance collective diffusion of Ni atoms across C regions may induce graphitization. It was shown that such a metal-driven graphitization is preferred to carbide formation when C is in excess 43 which explains also the absence of carbide formation in the temperature range applied. Once initiated the graphitization due to Ni diffusion proceeds even at RT as evidenced by 8 increase of the ML period which was observed on the sample annealed at 300 C after a 16-month RT storage. 24 Multilayers .